Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$84.33	12.516%	$94.8847	$94.88	$94.90	$94.90
Purchase #2	$229.49	3.766%	$238.1326	$238.13	$238.15	$238.10
Purchase #3	$174.51	7.302%	$187.2527	$187.25	$187.25	$187.30
Purchase #4	$152.46	12.183%	$171.0342	$171.03	$171.05	$171.00
Purchase #5	$70.92	10.320%	$78.2389	$78.24	$78.25	$78.20
Purchase #6	$112.81	11.325%	$125.5857	$125.59	$125.60	$125.60
Purchase #7	$51.36	4.821%	$53.8361	$53.84	$53.85	$53.80
7 purchase totals =	$875.88		$948.9649	$948.96	$949.05	$948.90